For the purpose of more efficient use of limited radio resources, multi antenna wireless communication systems are attracting attention and are now in progress of active research. Multi antenna wireless communication systems can acquire a gain of signal transmission and reception performance through beamforming using a plurality of antennas. Also, multi antenna wireless communication systems can acquire a spatial multiplexing and space diversity gain using a Multiple Input Multiple Output (MIMO) technology.
Scheduling techniques of multi antenna wireless communication systems are divided into two as follows:
First is a scheduling scheme using Channel State Information (CSI) wherein the CSI fed back, that is, an accurate channel state value is collected from a receiving stage and an optimal receiving-stage combination or an optimal stream combination is determined.
Second is a scheduling scheme using Channel Quality Information (CQI) wherein the CQI, that is, approximate channel information is collected from a receiving stage and scheduling is performed.
The scheduling scheme using CSI can employ Dirty Paper Coding (DPC) and beamforming ensuring a high reception success rate in a physical layer, however, has a disadvantage of generating many overheads because of a number of data amount of CSI. For example, a transmission stage bears a burden of having to feed back a channel matrix of a size of Nt×Nr in cases where the transmission stage uses Nt number of transmit antennas and a reception stage uses Nr number of receive antennas. The scheduling scheme using CQI can employ Space Time Coding (STC) and opportunistic beamforming. The STC and opportunistic beamforming cannot ensure as much high reception success rate as the DPC and beamforming, however, have an advantage that a relatively small size of feedback information is required.
Scheduling complexity can be judged from calculation complexity and required feedback information amount. In the multi antenna wireless communication system, the scheduling complexity is generally increased proportional to number of transmit/receive antennas. Therefore, there is needed an alternative for reducing the scheduling complexity.